During execution of dental treatment, when a tooth suffers a disease such as dental caries, the affected portion is removed, and restoration treatment is executed using various prosthetic materials such as a metal, a dental composite resin, and a porcelain.
The dental prosthetic appliance needs to undergo surface polishing after modification of its shape. When the polished surface is rough or when a flaw is present therein, this causes coloring, and adhesion of dental plaque. When the surface of the prosthetic appliance is not smooth and glossy, high aesthetics cannot be acquired and the touch felt by the tongue of a patient is bad. Therefore, the patient may feel uncomfortable.
Recently, cases of restoration treatment using materials having higher aesthetics such as the dental composite resin and ceramic materials including the porcelain have increased because of the growth of the demand for aesthetics by the patients. However, these materials are materials difficult to polish, and are highly difficult to polish. For example, the dental composite resin includes a glass filler having high hardness and a resin having low hardness. A substance including plural composition components each having hardness different from each other as above is difficult to evenly polish, and causing the substance to have gloss in the final polishing stage is highly difficult. A ceramic material includes, in its configuring materials, raw materials such as minerals such as feldspar and quartz, or leucite, alumina, zirconia, and lithium disilicate. This material has high aesthetics and durability that maintains the aesthetics for a long time, and is therefore introduced mainly into self-pay treatment. The material however has a highly hard physical property to maintain its high durability. Therefore, the ceramic material is classified as a material difficult to polish.
At present, the polishing is executed using various polishing instruments after adjusting the shape and the articulation of the dental prosthetic appliance using an abrasive material including vitrified or electro-deposition diamond. The polishing is executed using, for example, a point type polishing instrument formed by mixing polishing abrasive grains and an elastomer-based binder resin and shaping the mixture in a point shape, a disc type polishing instrument formed by fixing polishing abrasive grains to a disc-shaped base material, or a sheet type polishing instrument formed by adhering polishing abrasive grains to the surface of a rectangular shaped sheet.
In a dental clinic, as to the above polishing instruments, a doctor selects a proper polishing instrument from the various types of polishing instrument corresponding to the case. For example, the disc type polishing instrument has a highly effective shape for polishing a flat portion such as the surface of a front tooth facing a lip because the disc type polishing instrument is in evenly contact with the flat portion. The sheet type polishing instrument has a rectangular shape suitable for polishing an interdental portion (adjacent surfaces), and polishing is executed by placing the instrument through the interdentium and causing the polishing layer to be in contact with the adjacent surfaces. For a molar, the point type polishing instrument is effective such as that having a bullet shape suitable for polishing a complicated-shaped portion. Types of these polishing instruments include one having a polishing layer and a shaft integrated with each other and a snap-on type one including a shaft detachable unit capable of being attached and detached to/from the shaft to be used in dental clinical duties.
However, sufficient gloss cannot be acquired using any of these methods and, after using any one of the above polishing instruments, the final polishing gives the gloss by puff polishing using a dedicated polishing paste. However, this polishing work needs a long time and the polishing steps are increased. Therefore, the treatment efficiency is low and the chair time is extended imposing loads on both of the operator and the patient. These problems similarly arise in the dental technical work. When the polishing work takes a long time, the load on the operator due to the increase of the working time period becomes significant. Therefore, a polishing instrument achieving a high polishing effect is demanded to reduce the working time period.
Patent Literature 1 discloses a technique of improving a polishing property by kneading fine ultra abrasive grains such as diamond in an elastic elastomer, fitting the kneaded mixture with a surface to be polished, and reducing vibrations generated during the polishing. Patent Literature 2 discloses a technique concerning a dental polishing instrument whose polishing property is improved by forming the instrument as a curved disc-shaped polishing instrument to cause the instrument to fit with not only a flat surface but also a curved tooth surface.
The polishing instruments according to the techniques described in Patent Literature 1 and Patent Literature 2 each improve the polishing property by causing its polishing layer to fit with the surface to be polished. In each of Patent Literature 1 and Patent Literature 2, however, a mechanism is not properly provided that causes the polishing sludge produced during the polishing to leave and no sufficient polishing effect tends to be acquired due to occurrence of a secondary flaw caused by clogging or continuous contact of the polishing sludge with the surface to be polished.
On the other hand, to solve the problem, a technique is disclosed of disposing an air hole portion that intentionally causes the polishing sludge to leave. For example, Patent Literature 3 discloses a technique of improving the polishing property by disposing recesses or holes in a polishing layer, reducing the friction heat produced during the polishing, and causing the polishing sludge to leave. However, the recesses or the holes are disposed in only a portion of the polishing instrument, and the removing effect is high for the polishing sludge concerning the polishing layer close to the recesses or the holes while this effect is degraded for the polishing layer far from the recesses or the holes. According to Patent Document 3, therefore, as a result, the occurrence of the secondary flaw due to the clogging or the polishing sludge is inevitable.
Patent Literature 4 discloses a technique concerning a disc (sheet)-shaped polishing instrument whose polishing layer has air holes formed therein and that can maintain a polishing effect by constant emergence of a newly produced surface. According to Patent Literature 4, however, the formed air holes are unable to be controlled to always have the same positions and the same size depending on the casting condition. The acquired polishing effect presents an individual difference and cannot be said to be stable. Because the air holds are disposed in the polishing layer, the clogging and occurrence of the secondary flaw due to the polishing sludge may be suppressed while the strength of the polishing instrument may be degraded.